1. Field of the Invention
This invention relates generally to an information recording system and, more particularly, is directed to apparatus for recording a video signal on a magnetic tape.
2. Description of the Prior Art
In one type of helical-scan VTR, a magnetic tape extends helically about the periphery of a guide drum over an angular range of slightly mcre than 180 degrees and is adapted to be moved or advanced in the longitudinal direction of the tape while at least a portion of the guide drum is rotated. Two rotary transducers or magnetic heads are mounted on the rotated portion of the guide drum so as to rotate with the latter and thereby repeatedly scan across the tape in a path at an angle to the longitudinal direction of the tape. In this manner, a video signal is recorded on the magnetic tape in successive, parallel skewed tracks, with each track generally having a field interval recorded therein and being formed of successive areas which correspond to respective line intervals of the video signal. In order to avoid interference due to cross-talk during a signal reproduction operation, that is, to avoid interference due to signals which are picked up by a scanning transducer from an adjacent track when a given track is scanned, one practice has been to provide guard bands to separate successive parallel tracks on the tape. Such guard bands essentially are "empty" of information so as to avoid cross-talk pick-up from such adjacent guard bands when a particular track is scanned.
However, the use of guard bands to separate successive tracks is a relatively inefficient usage of the record medium, that is, if the guard bands themselves could be provided with useful information, the overall recording density would be improved. Accordingly, it has been the practice to provide the two rotary magnetic heads with different azimuth angles. Hence, information is recorded in one track at one azimuth angle and information is recorded in the next adjacent track with a different azimuth angle. When the information in a track is reproduced by a rotary magnetic head having the same azimuth angle as that used for recording, the information recorded in the scanned track is reproduced with minimal attenuation, but because of azimuth loss, the cross-talk which is picked-up from the next adjacent track is substantially attenuated. In this manner, high density recording can be achieved in which adjacent parallel tracks on the magnetic tape are arranged in an abutting or partially overlapping relation with respect to each other.
As previously discussed, the magnetic heads are rotated to repeatedly scan across the tape in a path at an angle to the longitudinal direction of the tape. Accordingly, during the recording operation of the VTR, the angle between the scanning path, and hence each record track, and the longitudinal direction of the tape is dependent on the rotational speed of the rotary heads and also the speed at which the magnetic tape is longitudinally advanced. Thus, if the speed and direction of advancement of the magnetic tape are not the same during the reproducing operation as during the recording operation, then the scanning path of the magnetic heads during reproducing will not precisely follow or coincide with the record tracks on the tape during movement of the heads across the tape.
In the case of special reproducing modes, that is, slow-, still- and fast-motion reproduction, the tape speed during reproduction is different from the normal tape speed during recording. For example, during slow-motion reproduction, the magnetic heads rotate at a speed which is the same as that used in the normal reproducing mcde, while the magnetic tape is driven at a speed which is slower than that used in the normal reproducing mode. Accordingly, the rotating magnetic heads repeatedly scan the record tracks so as to reproduce a picture having a slower motion than it would have if reproduced in a normal reproducing mode. In like manner, during still-motion reproduction, a single track is repeatedly scanned by the rotating heads to produce a still-motion picture. However, the scanning direction by the magnetic heads is inclined with respect to the record tracks being scanned thereby and this inclination gives rise to a tracking deviation. In such case, one of the rotating heads having a first azimuth angle deviates from the track to be scanned thereby and scans a portion of the next adjacent track which had been recorded by the other rotating head having a different azimuth angle. This results in a noise bar in the reproduced picture.